Recently, it has become popular to process and manage the sound and video in digital format in appliances such as acoustic appliances and video appliances. Such trends in digital encoding of sound and video in appliances such as acoustic appliances are extending to the field of radio broadcasting. For example, in the United States, a digital radio broadcasting system called IBOC (In Band On Channel) is proposed and made available by iBiquity Digital Corp.
Meanwhile, conventional analog radio broadcasting broadcasts via carrier wave (hereinafter referred to as “analog carrier wave”) that has frequency distribution inside the frequency band (hereinafter referred to as “channel” or “frequency channel”) assigned to individual broadcasting stations. Actually, in order to avoid the interference between analog carrier wave of adjacent channels, only the center portion of the assigned band is used for the transmission of the analog carrier wave, and other portions are not used. It is noted that “digital radio broadcasting” in this application means “IBOC digital radio broadcasting”.
IBOC is a type of digital radio broadcasting that uses a frequency channel assigned to the conventional analog radio broadcasting. In IBOC standard, a plurality of signal formats are defined, such as a hybrid format in which the digital radio broadcasting signal is multiplexed onto the conventional analog radio broadcasting signal, and an all-digital format constituted by only digital signals, and it is designed to gradually transfer from conventional analog radio broadcasting to all-digital radio broadcasting that has many functions and is high in quality. In the IBOC, digital broadcasting signals are transmitted with Orthogonal Frequency Division Multiplexing (OFDM) that uses many carrier waves (subcarriers).
In the IBOC standard, a signal format called “hybrid format” is used in the transition period from analog broadcasting to all-digital broadcasting. In the hybrid format, the digital radio broadcasting, which allocates the subcarrier of digital broadcasting in the portion that is adjacent to the center portion of the band that the analog carrier wave uses and that was not conventionally used (hereinafter referred to as “sideband”) is broadcast using the modulated wave of the sideband of the band. In other words, in accordance with the hybrid format of the IBOC, the frequency band assigned for the conventional analog radio broadcasting is utilized effectively, and the analog radio broadcasting and the digital radio broadcasting are simultaneously transmitted using a same channel.
For example, Japanese Patent Provisional Publication No. JP2005-191850A (hereinafter referred to as “the Reference Document”) discloses an IBOC broadcasting receiver that is capable of receiving such IBOC digital radio broadcasting. The IBOC broadcasting receiver disclosed in the Reference Document is provided with an automatic seek function for seeking receivable channel.
The IBOC broadcasting receiver starts channel seeking operation when a predetermined user operation (e.g., pressing down once the “Tuning up” or “Tuning down” button equipped at the operation panel.) is performed, and the receiving intensity of the seeking channel is detected. When it is set in a first seek mode, the IBOC broadcasting receiver determines the channel station-existent if the detected receiving intensity is higher than a predetermined amount, and selects the channel, and the channel seeking operation is ceased. Further, when it is set in a second seek mode, the broadcasting receiver performs the decoding process of the digital broadcasting signal along with the channel seeking operation. Then, referring to the result of the process, it determines whether the digital radio broadcasting is performed in the channel. Only when it is determined that the digital radio broadcasting is performed, the channel is selected and the channel seeking operation is ceased. Thereby, the digital radio broadcasting is played.